1. Field of the Invention
The present invention relates to a device and method for adjusting the degree of mixing in mixing equipment such as, for example, an extruder or a continuous mixer.
2. Description of the Related Art
Generally, a composite resin material, e.g., plastic compound, is produced by feeding pellets or powder of a polymer resin as a matrix, as well as an admixture, into a barrel of mixing equipment such as an extruder or a continuous mixer, and feeding the two to a downstream side while mixing the two with kneading/mixing screws inserted into the barrel. The longer the material is stayed, allowing mixing to proceed, in a mixing section within the barrel, the higher becomes the degree of mixing of material in the mixing equipment. Therefore, in the conventional extruder or continuous mixer, a mixing degree adjusting device equipped with a gate member for damming up material is provided downstream of a mixing section. The degree of material retention is changed by opening or closing the gate member, thereby changing a pressure difference ΔP across the gate member to adjust the degree of mixing.
As such mixing degree adjusting devices there are known, for example, those disclosed in Japanese Patent No. 3854298 and Japanese Patent Laid-Open Publication No. Hei 10 (1998)-305422. The mixing degree adjusting devices disclosed therein each have a portion of a circular section formed in a cylindrical shape at an intermediate position axially of each kneading/mixing screw. Further, through a barrel at an axial position corresponding to the portion of a circular section there is provided a gate member for changing the flow path area of material with respect to the portion of a circular section.
The gate member described in each of the above patent literatures can move toward and away from the portion of a circular section. When the gate member is moved toward the portion of a circular section, material stays in a mixing section and a pressure difference ΔP across the gate member becomes large, so that the degree of mixing becomes high. When the gate member is moved away from the portion of a circular section, the material becomes easier to flow and the pressure difference ΔP becomes small, so that the degree of mixing becomes low.
In the mixing degree adjusting devices disclosed in the foregoing patent literatures, the change in the pressure difference ΔP across the gate member is not linear relative to a drive quantity, x, of gate member drive means. In other words, the degree of mixing changes in a non-linear manner relative to the drive quantity, x, of the gate member drive means. For example, in the case where the degree of opening, δ, of the gate member is small, even a slight movement of the gate member would lead to a sudden increase of flow path area, so that pressure difference ΔP (i.e., the degree of mixing) is suddenly changed. However, in case of the gate member opening, δ, being large, even a slight movement of the gate member would not cause a great change in both flow path area and pressure difference ΔP.
That is, the pressure difference ΔP shows a certain linear correlativity with respect to the flow path area of material, but is non-linear with respect to the degree of opening, δ, of the gate member. As a matter of course, in the mixing degree adjusting device disclosed in each of the foregoing patent literatures in which the degree of opening, δ, of the gate member, in other words, a movement quantity, Δδ, of the gate member relative to the portion of a circular section, is changed at a certain change rate, the gate operability is poor when adjusting the flow path area at the beginning of opening of the gate member (e.g., in a range up to a degree of opening of 1 mm or so), and it is difficult to make a stable adjustment of the pressure difference, ΔP, (i.e., the degree of mixing).